The present invention relates to a method of feeding a coating liquid from a coating liquid tank to a coating apparatus through a filter and a degassing apparatus by a feeding pump.
In the prior art, as described in Japanese Patent Examined Publication No. 43722/1987, gas in a path of a coating liquid is driven away by using water degassed in advance as a cleaning liquid and by supplying the cleaning liquid in the path successively for a considerable time to prevent from bubble trouble happening after pouring a coating liquid in the path.
However, in the case of pouring the degassed water as cleaning liquid in the path including a filter of removing foreign substances in a coating liquid, bubbles attached to the filter made of organic macromolecule fiber such as polypropylene and cellulose etc., are eluted in the cleaning liquid, are scattered in the path after the filter and are caught easily by a non-hydrophilic material such as packing members provided at joints of pipes, by cracks in the inside of the pipes and the like. Further, the degassed water does not have so high wettability to the filter as the coating liquid, so that it is difficult to remove the bubbles sufficiently. Therefore, if the coating liquid is poured in the path after the degassed water is poured in the path as described above, the remaining bubbles in the filter or the bubbles trapped in the pipes mix into the coating liquid again, and cause the bubble trouble on the substrates coated with the coating liquid.
Therefore, according to the prior art, a considerably long time is required to clean the inside of the pipes.